CHAPTER 1 INTRODUCTION TO MINERALOGY Petrophysics is the study of rock properties and their interactions with fluids (gases,liquid hydrocarbons,and aqueous solutions).The geologic material forming a reservoir for the accumulation of hydrocarbons in the subsurface must contain a three-dimensional network of interconnected pores in order to store the fluids and allow for their movement within the reservoir.Thus the porosity of the reservoir rocks and their permeability are the most fundamental physical properties with respect to the storage and transmission of fluids.Accurate knowledge of these two properties for any hydrocarbon reservoir,together with the fluid properties,is required for efficient development,management,and prediction of future performance of the oilfield. The purpose of this text is to provide a basic understanding of the physical properties of porous geologic materials,and the interactions of various fluids with the interstitial surfaces and the distribution of pores of various sizes within the porous medium.Procedures for the measurement of petrophysical properties are included as a necessary part of this text. Applications of the fundamental properties to subsurface geologic strata must be made by analyses of the variations of petrophysical properties in the subsurface reservoir. Emphasis is placed on the testing of small samples of rocks to uncover their physical properties and their interactions with various fluids.A considerable body of knowledge of rocks and their fluid flow properties has been obtained from studies of artificial systems such as networks of pores etched on glass plates,packed columns of glass beads, and from outcrop samples of unconsolidated sands,sandstones,and limestones.These studies have been used to develop an understanding 1
CHAPTER 1 INTRODUCTION TO M I N ERALOGY Petrophysics is the study of rock properties and their interactions with fluids (gases, liquid hydrocarbons, and aqueous solutions). The geologic material forming a reservoir for the accumulation of hydrocarbons in the subsurface must contain a three-dimensional network of interconnected pores in order to store the fluids and allow for their movement within the reservoir. Thus the porosity of the reservoir rocks and their permeability are the most fundamental physical properties with respect to the storage and transmission of fluids. Accurate knowledge of these two properties for any hydrocarbon reservoir, together with the fluid properties, is required for efficient development, management, and prediction of future performance of the oilfield. The purpose of this text is to provide a basic understanding of the physical properties of porous geologic materials, and the interactions of various fluids with the interstitial surfaces and the distribution of pores of various sizes within the porous medium. Procedures for the measurement of petrophysical properties are included as a necessary part of this text. Applications of the fundamental properties to subsurface geologic strata must be made by analyses of the variations of petrophysical properties in the subsurface reservoir. Emphasis is placed on the testing of small samples of rocks to uncover their physical properties and their interactions with various fluids. A considerable body of knowledge of rocks and their fluid flow properties has been obtained from studies of artificial systems such as networks of pores etched on glass plates, packed columns of glass beads, and from outcrop samples of unconsolidated sands, sandstones, and limestones. These studies have been used to develop an understanding 1
2 PETROPHYSICS:RESERVOIR ROCK PROPERTIES of the petrophysical and fluid transport properties of the more complex subsurface samples of rocks associated with petroleum reservoirs. This body of experimental data and production analyses of artificial systems,surface rocks,and subsurface rocks make up the accumulated knowledge of petrophysics.Although the emphasis of this text is placed on the analyses of small samples,the data are correlated to the macroscopic performance of the petroleum reservoirs whenever applicable.In considering a reservoir as a whole,one is confronted with the problem of the distribution of these properties within the reservoir and its stratigraphy.The directional distribution of thickness,porosity, permeability,and geologic features that contribute to heterogeneity governs the natural pattern of fluid flow.Knowledge of this natural pattern is sought to design the most efficient injection-production system for economy of energy and maximization of hydrocarbon production (1]. Petrophysics is intrinsically bound to mineralogy and geology because the majority of the world's petroleum occurs in porous sedimentary rocks.The sedimentary rocks are composed of fragments of other rocks derived from mechanical and chemical deterioration of igneous, metamorphic,and other sedimentary rocks,which is constantly occurring.The particles of erosion are frequently transported to other locations by winds and surface streams and deposited to form new sedimentary rock structures.Petrophysical properties of the rocks depend largely on the depositional environmental conditions that controlled the mineral composition,grain size,orientation or packing, amount of cementation,and compaction. MINERAL CONSTITUENTS OF ROCKS-A REVIEW The physical properties of rocks are the consequence of their mineral composition.Minerals are defined here as naturally occurring chemical elements or compounds formed as a result of inorganic processes.The chemical analysis of six sandstones by emission spectrography and X-ray dispersive scanning electron microscopy [2]showed that the rocks are composed of just a few chemical elements.Analysis of the rocks by emission spectroscopy yielded the matrix chemical composition since the rocks were fused with lithium to make all of the elements soluble in water,and then the total emission spectrograph was analyzed. The scanning electron microscope X-ray,however,could only analyze microscopic spots on the broken surface of the rocks.The difference between the chemical analysis of the total sample and the spot surface analysis is significant for consideration of the rock-fluid interactions.The presence of the transition metals on the surface of the rocks induces
2 PETROPHYSICS: RESERVOIR ROCK PROPERTIES of the petrophysical and fluid transport properties of the more complex subsurface samples of rocks associated with petroleum reservoirs. This body of experimental data and production analyses of artificial systems, surface rocks, and subsurface rocks make up the accumulated knowledge of petrophysics. Although the emphasis of this text is placed on the analyses of small samples, the data are correlated to the macroscopic performance of the petroleum reservoirs whenever applicable. In considering a reservoir as a whole, one is confronted with the problem of the distribution of these properties within the reservoir and its stratigraphy. The directional distribution of thickness, porosity, permeability, and geologic features that contribute to heterogeneity governs the natural pattern of fluid flow. Knowledge of this natural pattern is sought to design the most efficient injection-production system for economy of energy and maximization of hydrocarbon production [ 13. Petrophysics is intrinsically bound to mineralogy and geology because the majority of the world’s petroleum occurs in porous sedimentary rocks. The sedimentary rocks are composed of fragments of other rocks derived from mechanical and chemical deterioration of igneous, metamorphic, and other sedimentary rocks, which is constantly occurring. The particles of erosion are frequently transported to other locations by winds and surface streams and deposited to form new sedimentary rock structures. Petrophysical properties of the rocks depend largely on the depositional environmental conditions that controlled the mineral composition, grain size, orientation or packing, amount of cementation, and compaction. MINERAL CONSTITUENTS OF ROCKS-A REVIEW The physical properties of rocks are the consequence of their mineral composition. Minerals are defined here as naturally occurring chemical elements or compounds formed as a result of inorganic processes. The chemical analysis of six sandstones by emission spectrography and X-ray dispersive scanning electron microscopy [2] showed that the rocks are composed of just a few chemical elements. Analysis of the rocks by emission spectroscopy yielded the matrix chemical composition since the rocks were fused with lithium to make all of the elements soluble in water, and then the total emission spectrograph was analyzed. The scanning electron microscope X-ray, however, could only analyze microscopic spots on the broken surface of the rocks. The difference between the chemical analysis of the total sample and the spot surface analysis is significant for consideration of the rock-fluid interactions. The presence of the transition metals on the surface of the rocks induces
MINERAL CONSTITUENTS OF ROCKS-A REVIEW 3 preferential wetting of the surface by oil through Lewis acid-base type reactions between the polar organic compounds in crude oils and the transition metals exposed in the pores [3].The high surface concentration of aluminum reported in Table 1.1 is probably due to the ubiquitous presence of clay minerals in sandstones. The list of elements that are the major constituents of sedimentary rocks (Table 1.1)is confirmed by the averages of thousands of samples of the crust reported by Foster [4](Table 1.2).Just eight elements make up 99%(by weight)of the minerals that form the solid crust of the earth; these are the elements,including oxygen,listed in the first seven rows of TABLE 1.1 AVERAGE OF THE COMPOSITIONS OF SIX SANDSTONE ROCKS(REPORTED AS OXIDES OF CATIONS)OBTAINED BY EMISSION SPECTROSCOPY AND THE SCANNING ELECTRON MICROSCOPE [2] Surface Analysis Total Analysis (Scanning Electron (Emission Spectrograph) Microscope) Silicon oxide (SiO2) 84.1 69.6 Aluminum oxide(Al2O3) 5.8 13.6 Sodium oxide (NaO) 2.0 0.00 Iron oxide (Fe203) 1.9 10.9 Potassium oxide (K2O) 1.1 3.0 Calcium oxide (CaO) 0.70 2.1 Magnesium oxide (MgO) 0.50 0.00 Titanium oxide (TiO) 0.43 1.9 Strontium oxide (SrO) 0.15 0.00 Manganese oxide (MnO) 0.08 2.0 TABLE 1.2 WEIGHT AND VOLUME OF THE PRINCIPAL ELEMENTS IN THE EARTH'S CRUST Element Weight Percent Volume Percent Oxygen 46.40 94.05 Silicon 28.15 0.88 Aluminum 8.23 0.48 Iron 5.63 0.48 Calcium 4.15 1.19 Sodium 2.36 1.11 Magnesium 2.33 0.32 Potassium 2.09 1.49 (Courtesy C.E.Merrill Publishing Co.,Columbus,OH.)
MINERAL CONSTITUENTS OF ROCKS-A REVIEW 3 preferential wetting of the surface by oil through Lewis acid-base type reactions between the polar organic compounds in crude oils and the transition metals exposed in the pores [3]. The high surface concentration of aluminum reported in Table 1.1 is probably due to the ubiquitous presence of clay minerals in sandstones. The list of elements that are the major constituents of sedimentary rocks (Table 1.1) is confirmed by the averages of thousands of samples of the crust reported by Foster [4] (Table 1.2). Just eight elements make up 99% (by weight) of the minerals that form the solid crust of the earth; these are the elements, including oxygen, listed in the first seven rows of TABLE 1.1 AVERAGE OF THE COMPOSITIONS OF SIX SANDSTONE ROCKS (REPORTED AS OXIDES OF CATIONS) OBTAINED BY EMISSION SPECTROSCOPY AND THE SCANNING ELECTRON MICROSCOPE [2] Surface Analysis Total Analysis (Scanning Electron (Emission Spectrograph) Microscope) Silicon oxide (Si02) Aluminum oxide (Al2O3) Sodium oxide (NaO) Iron oxide (FezO3) Potassium oxide (K20) Calcium oxide (CaO) Magnesium oxide (MgO) Titanium oxide (TiO) Strontium oxide (SrO) Manganese oxide (MnO) 84.1 5.8 2.0 1.9 1.1 0.70 0.50 0.43 0.15 0.08 69.6 13.6 0.00 10.9 3.0 2.1 0.00 1.9 0.00 2.0 TABLE 1.2 WEIGHT AND VOLUME OF THE PRINCIPAL ELEMENTS IN THE EARTH’S CRUST Element Weight Percent Volume Percent Oxygen Silicon Aluminum Iron Calcium Sodium Magnesium Potassium 46.40 28.15 8.23 5.63 4.15 2.33 2.09 2.36 94.05 0.88 0.48 0.48 1.19 1.11 0.32 1.49 (Courtesy C.E. Merrill Publishing Co., Columbus, OH.)
4 PETROPHYSICS:RESERVOIR ROCK PROPERTIES Table 1.1 from analysis of six sandstones.Although the crust appears to be very heterogeneous with respect to minerals and types of rocks,most of the rock-forming minerals are composed of silicon and oxygen together with aluminum and one or more of the other elements listed in Table 1.2. The chemical compositions and quantitative descriptions of some minerals are listed in Tables 1.3 and 1.4.Some of the minerals are very TABLE 1.3 LIST OF THE PRINCIPAL SEDIMENTARY ROCKS Sedimentary Rocks Mechanism Formation Composition Mechanical Sandstone Quartzose-Quartz grains,deltaic in origin weathering Arlkosic-20%+feldspar grains Graywacke-Poorly sorted grains of other rocks with feldspar and clay Calcareous-Fragments of limestone Friable sand Clastics-Loosely cemented grains of other rocks Unconsolidated Clastics-Loose sand-grains from other sand rocks Siltstone Clastics-Compacted,cemented,fine- grained clastics with grain size less than 1/16mm Conglomerate Garvel and boulders cemented with mud and fine sand Chemical Shale Clay-Compacted fine-grain particles with weathering grain size less than 1/256 mm.Usually laminated in definite horizontal bedding planes.As oil shale it contains organic matter (kerogen). Evaporites Salts and some limestone -Gypsum (CaSO42H2O) -Anhydrite (CaSO) -Chert (SiO2) -Halite (NaCl) -Limestone (CaCO3) Dolomite Carbonate-Chemical reaction with limestone (CaMg(CO3)2) Limestone Carbonate-Biological extraction of calcium and precipitation of CacO3 Biological Reefs Carbonate-Fossil remains of marine origin organisms Diatomite Silicates-Silicate remains of microscopic plants
4 PETROPHYSICS: RESERVOIR ROCK PROPERTIES Table 1.1 from analysis of six sandstones. Although the crust appears to be very heterogeneous with respect to minerals and types of rocks, most of the rock-forming minerals are composed of silicon and oxygen together with aluminum and one or more of the other elements listed in Table 1.2. The chemical compositions and quantitative descriptions of some minerals are listed in Tables 1.3 and 1.4. Some of the minerals are very TABLE 1.3 LIST OF THE PRINCIPAL SEDIMENTARY ROCKS Sedimentary Rocks Mechanism Mechanical weathering Chemical weathering Biological origin Formation Sandstone Friable sand Unconsolidated sand Siltstone Conglomerate Shale Evaporites Dolomite Limestone Reefs Diatomite Composition Quartzose-Quartz grains, deltaic in origin ArIkosic-20% + feldspar grains Graywacke-Poorly sorted grains of other rocks with feldspar and clay Calcareous-Fragments of limestone Clastics-Loosely cemented grains of other Clastics-Loose sand-grains from other Clastics-Compacted, cemented, finerocks rocks grained clastics with grain size less than 1/16 mm Garvel and boulders cemented with mud and fine sand Clay-Compacted fine-grain particles with grain size less than 1/256 111111. Usually laminated in definite horizontal bedding planes. As oil shale it contains organic matter (kerogen). Salts and some limestone -Gypsum (Cas04 2H2 0) -Anhydrite (CaSO4) -Chert (SiOz) -Halite (NaC1) -Limestone (CaC03) limestone (CaMg(CO3)z) calcium and precipitation of CaC03 organisms plants Carbonate-Chemical reaction with Carbonate-Biological extraction of Carbonate-Fossil remains of marine Silicates-Silicate remains of microscopic
TABLE 1.4 MINERAL COMPOSITIONS AND DESCRIPTIONS.PARENTHESES IN THE FORMULAS MEAN THAT THE ELEMENTS ENCLOSED MAY BE PRESENT IN VARYING AMOUNTS. Agate (Chalcedony)-SiO2:silicon dioxide;variable colors:waxy luster:H=7*. Anhydrite-CaSO4:calcium sulfate;white-gray;H=2. Apatite-Cas(PO)3F:fluorapatite;H=4. Asbestos (Serpentine)-Mg6SisO1o(OH)s:hydrous magnesium silicate:light green to dark gray;greasy or waxy;H 3. Augite (Pyroxene group)-(Ca,Na)(Al,Fe2+,Fe,Mg)(Si,AD)2O6:Alkali,ferro- magnesium,aluminum silicates;dark green to black;exhibits cleavage;large, complex group of minerals;H=5. Barite-BaSO:barium sulfate;white,light blue,yellow.or red;pearly luster, H=3. Beryl-Be;Al2Si6O18:clear beryl forms the blue-green aquamarine and green emerald gems;exhibits cleavage.Beryl is an ore of the element beryllium: H=7-8. Biotite (Mica)-K(Fe,Mg)s(AlSi3O10)(OH)2:hydrous potassium, ferro- magnesium,aluminum silicate;dark green to black (black mica);vitreous; exhibits cleavage;rock-forming mineral:H=3. Calcite-CacO:calcium carbonate:colorless or white to light brown.vitreous: effervesces in dilute HCl;H 3. Celestite-SrSO4:strontium sulfate;colorless;H 3. Chalk-CacOs:calcite;white:soft fine-grained limestone formed from microscopic shells;effervesces with dilute HCl;H =2-3. Chlorite-(Al,Fe,Mg)6(Al,Si)4O10(OH)8:hydrous ferro-magnesium,aluminum silicate;shades of green (green mica);exhibits cleavage;rock-forming mineral: H=3. Cinnabar-HgS:mercury sulfide;red to brownish-red;luster is dull.Only important ore of mercury:H=2.5. Cordierite-Al4(Fe,Mg)2SisO18:ferro-magnesium aluminum silicate;blue: vitreous;H=7. Corundum-Al2O3:red varieties are rubies and other colors are known as sapphire;H=9. Diatomite-SiOz:silica;white;formed from microscopic shells composed of silica:distinguished from chalk by lack of effervescence with dilute HCl: H=1-2 Dolomite-CaMg(CO3)2:calcium-magnesium carbonate:pink or light brown, vitreous-pearly:effervesces in HCI if powdered;H =3. Feldspar (Orthoclase,Potassium feldspar)-KalSi3Og:white to pink;vitreous: large crystals with irregular veins;exhibits cleavage;rock-forming mineral; H=6. Feldspar (Plagioclase)-CaAl2Si2Og and NaAlSisOg(Albite):calcium and sodium aluminum silicate;white to green;vitreous;exhibits cleavage:rock-forming mineral:H=6. Fluorite-CaF2:calcium fluorite;H =4. Galena-PbS:lead sulfide;lead-gray;bright metallic luster;lead ore;H=2.5. *H =Hardness;defined in the Glossary. Continued
TABLE 1.4 MINERAL COMPOSITIONS AND DESCRIPTIONS. PARENTHESES IN THE FORMULAS MEAN THAT THE ELEMENTS ENCLOSED MAY BE PRESENT IN VARYING AMOUNTS. Agate (Chalcedony)-SiO2: silicon dioxide; variable colors; waxy luster; H = 7*. Anhydrite-CaS04: calcium sulfate; white-gray; H = 2. Apatite-Cag(PO4)gF: fluorapatite; H = 4. Asbestos (Serpentine)-Mg6Si4010(0H)~: hydrous magnesium silicate; light green to dark gray; greasy or waxy; H = 3. Augite (Pyroxene group)-(Ca, Na)(Al, Fe2+, Fe3+, Mg)(Si, Al)zO6: Alkali, ferromagnesium, aluminum silicates; dark green to black; exhibits cleavage; large, complex group of minerals; H = 5. Barite-BaS04: barium sulfate; white, light blue, yellow, or red; pearly luster, H = 3. Beryl-Be3d2Si6018: clear beryl forms the blue-green aquamarine and green emerald gems; exhibits cleavage. Beryl is an ore of the element beryllium; Biotite (Mica)-K(Fe, Mg)3(AlSi3010)(OH)z: hydrous potassium, ferromagnesium, aluminum silicate; dark green to black (black mica); vitreous; exhibits cleavage; rock-forming mineral; H = 3. Calcite-CaCO3: calcium carbonate; colorless or white to light brown, vitreous; effervesces in dilute HC1; H = 3. Celestite-SrS04: strontium sulfate; colorless; H = 3. Chalk-CaC03 : calcite; white; soft fine-grained limestone formed from microscopic shells; effervesces with dilute HCl; H = 2-3. Chlorite-(Al, Fe, Mg)6(Al, Si)4010(OH)8: hydrous ferro-magnesium, aluminum silicate; shades of green (green mica); exhibits cleavage; rock-forming mineral; H = 3. Cinnabar-HgS: mercury sulfide; red to brownish-red; luster is dull. Only important ore of mercury; H = 2.5. Cordierite-Al4(Fe, Mg)z Si5 0 18 : ferro-magnesium aluminum silicate; blue; vitreous; H = 7. Corundurn-Al203: red varieties are rubies and other colors are known as sapphire; H = 9. Diatomite-Si02 : silica; white; formed from microscopic shells composed of silica; distinguished from chalk by lack of effervescence with dilute HCl; D0lomite-CaMg(CO3)~: calcium-magnesium carbonate; pink or light brown, vitreous-pearly; effervesces in HCl if powdered; H = 3. Feldspar (Orthoclase, Potassium feldspar)-KalSi308: white to pink; vitreous; large crystals with irregular veins; exhibits cleavage; rock-forming mineral; H = 6. Feldspar (Plagioclase)-CaAl~Si208 and NaAlSi308(dbite): calcium and sodium aluminum silicate; white to green; vitreous; exhibits cleavage; rock-forming mineral; H = 6. H = 7-8. H = 1-2. Fluorite-CaF2: calcium fluorite; H = 4. Galena-PbS: lead sulfide; lead-gray; bright metallic luster; lead ore; H = 2.5. *H = Hardness; defined in the Glossary. Continued